1. Field of the Invention
The present invention relates, in general, to clamps and, more specifically, to pivotal clamps for holding a workpiece during manufacturing operations.
2. Background Description
Clamps are widely employed to hold two or more parts together during a manufacturing operation. In automotive assembly plants, for example, clamps are used to hold two or more metal sheets or parts together under pressure and at a predetermined coordinate position during welding, piercing, hemming and other manufacturing operations.
Typically, such clamps include a riser which is mounted via a mounting plate to a tool base. A clamp with at least one pivotal clamp arm is mounted on the upper end of the riser and is movable between an open position and a closed, workpiece engaging position, either manually or under power by means of a fluid cylinder, for example. In such a clamp, two pressure feet or N/C blocks are respectively mounted on one end of the clamp arm through a clamp nose member attached to the pivotal clamp arm and to the upper end of the riser to establish a predetermined coordinate position therebetween when the clamp arm is moved to the closed position bringing the pressure feet into engagement with the workpiece.
Due to close tolerances required for accurate automobile assembly, the pressure feet, clamp arm and clamp nose are usually specifically designed and machined to specified dimensions and tolerances for each application. A typical clamp construction includes a clamp nose having a slot extending inward from one end which engages opposite side walls of one end of the pivotal clamp arm. All mating surfaces on the clamp arm and the clamp nose require machining to insure accurate final assembly dimensions when the clamp nose is welded to the clamp arm. Furthermore, the pressure foot is attached to the opposite end of the clamp nose either directly or indirectly by means of an intermediate mounting bracket. Again, all mating surfaces between the clamp nose and the pressure foot require precision machining for accurate buildup dimensions in the clamp.
These special clamp parts require additional design time to create drawings for each part of each clamp. Additional time is also required to machine each part to the prescribed dimensions prior to assembly of the clamp. All of such design and machining time contributes to the cost of the clamp. Furthermore, at final assembly, dimensional differences between the clamp and the sheet metal often require additional machining and/or the use of shims to position the pressure feet at the desired coordinate positions.
Thus, it would be desirable to provide a clamp for manufacturing operations which is constructed of as many standard parts as possible so as to reduce design, construction and assembly time of the clamp. It would also be desirable to provide a clamp which can be loosely assembled prior to welding of the clamp parts in the desired coordinate positions at final assembly of the clamp at the use site.